The present invention relates to a heater, such as a ceramic heater or a sheath heater, particularly of the kind suitable for a glow plug and an engine coolant heating device.
Hereinafter, the term xe2x80x9cfrontxe2x80x9d refers to a heating end side with respect to the axial direction of a heater, and the term xe2x80x9crearxe2x80x9d refers to a side opposite the front side.
A glow plug is mounted in the cylinder head of a diesel engine for attaining a rapid starting of the engine. The glow plug includes a heater generally provided with a cylindrical metallic shell, a rod-shaped heater body disposed in a front portion of the metallic shell with a front end portion of the heater body protruded from the metallic shell and an electrode disposed in a rear portion of the metallic shell for power supply to the heater body. The heater body and the electrode are positioned so as to provide a space between a rear end surface of the heater body and a front end surface of the electrode, and a front end portion of the electrode is electrically connected to a rear end portion of the heater body via a metallic lead wire. Further, a rear end portion of the electrode is protruded from the metallic shell. A terminal member is fitted onto the protruded rear end portion of the electrode by e.g. caulking so as to be detachably capped with a connector with a harness. In such a structure, the heater body is externally energized through the connector, the terminal member, the electrode and the lead wire.
It is now noted that the heater requires good electrical conductivity from the terminal member to the heater body for the purpose of improving the heat generating efficiency of the heater.
However, the electrical connection between the electrode and the terminal member is attained by caulking the terminal member to the electrode in the above structure, and such caulked portions are rust-prone to increase a contact resistance in the connection between the electrode and the terminal member over time. Thus, there often arise problems of high power loss and undesired heat generation at such a connection. Further, the terminal member needs to have a particular configuration for mating and unmating with the connector, and be knurled to strengthen the connection between the terminal member and the electrode. As a result, much time and effort are required for the production of the heater, which results in increase in production cost
It is therefore an object of the present invention to provide a heater which can be easily produced with a simple structure and attain good electrical conduction from the terminal member to the heater body throughout an extended period of time. Particularly, such a heater can be embodied as a ceramic heater in which a heating element is embedded in a ceramic substrate or a sheath heater in which a heating element is accommodated in a metallic sheath tube, which are suitable for a glow plug and an engine coolant heating device.
According to a first aspect of the present invention, there is provided a heater comprising: a cylindrical metallic shell; a heater body partly disposed in a front end portion of the metallic shell; an electrode disposed in a rear portion of the metallic shell and electrically connected to the heater body; and a terminal adapted to be capped with an electric connector, the terminal having a terminal body to be directly brought into electrical connection with the electric connector for power supply to the heater body through the electrode and an engaging portion formed on an outer circumferential surface of the terminal body so as to be engageable with the electric connector, the electrode and the terminal body being formed integrally with each other.
According to a second aspect of the present invention, there is provided a heater comprising: a metallic shell; a heater body partly disposed in a front end portion of the metallic shell; a conductive rod disposed in a rear portion of the metallic shell such that a rear end portion of the conductive rod is protruded from the metallic shell, the conductive rod being a single piece and electrically connected at a front end portion thereof to the heater body for power supply to the heater body; and an engagement protrusion formed radially outward on an outer circumferential surface of the protruded rear end portion of the conducting rod so as to be engageable with an electric connector and thereby make a direct electrical connection between the conductive rod and the electric connector.